1. Field of the Invention
The present invention relates to a production technology for obtaining polycrystalline silicon by reacting trichlorosilane (TCS) with hydrogen.
2. Description of the Related Art
In a process for producing high-purity polycrystalline silicon of a semiconductor grade, generally a “Siemens method” of reducing a trichlorosilane (TCS) gas and depositing the product on a silicon rod has been widely used.
As for the Siemens method, National Publication of International Patent Application No. 2004-532786 (Patent Document 1) discloses an invention relating to a method of producing polycrystalline silicon, which newly includes a step of converting disilane (HnCl6−nSi2: n is a value of 0 to 6) that exists in a gaseous effluent coming out from a CVD process for producing polycrystalline silicon, into mono-silane, in a hydrogenation reaction vessel for converting tetrachlorosilane (STC) into trichlorosilane (TCS). The method is evaluated to have advantages of enhancing a yield of a hydrogenation process by combining a hydrogenation reaction with a thermal decomposition reaction of disilane in the same reaction vessel which is the hydrogenation reaction vessel, and the like.
Incidentally, a by-product mixture produced when polycrystalline silicon is deposited by reacting TCS with hydrogen also includes a poly-silane (H2(n+1)−mClmSin: n is an integer of 3 or 4 and m is an integer of 0 to 2(n+1)), other than disilane having a silicon atom number n of 2. Accordingly, if these poly-silanes can be effectively used, the by-product mixture produced in the step of depositing the polycrystalline silicon is facilitated to be recycled as a raw material for producing the polycrystalline silicon, and a yield of the production process is further enhanced.
In other words, a conventional method of producing polycrystalline silicon including a method disclosed in National Publication of International Patent Application No. 2004-532786 (Patent Document 1) has a room to be improved in a process of converting the above described by-product mixture into a raw material for producing the polycrystalline silicon.
In addition, in order to produce high-purity polycrystalline silicon of a semiconductor grade, it is required to enhance the purity of TCS which is to be the raw material. As a result, it is needed to prepare a step for removing impurities in the TCS and the by-product which are circulated and used in the process for producing the polycrystalline silicon. Accordingly, it is extremely important from a practical standpoint to design the process so as to facilitate the removal of impurities from the TCS and the by-product which are circulated and used in the process for producing the polycrystalline silicon.